1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device selectively using reflective and transmissive modes and having equivalent light efficiency and color reproducibility in reflective and transmissive portions, and a fabricating method thereof.
2. Discussion of the Related Art
Generally, transflective liquid crystal display (LCD) devices function as both transmissive and reflective LCD devices. Because the transflective LCD devices can use both a backlight and the exterior natural or artificial light, the transflective LCD devices are usable in more circumstances, and power consumption of transflective LCD devices can be reduced.
FIG. 1 is a schematic plane view of an array substrate for a transflective liquid crystal display device according to the related art. A gate line 52 and a data line 62 are formed on a substrate 50. A gate line 52 and a data line 62 cross each other to define a pixel region “P.” A thin film transistor (TFT) “T,” including a gate electrode 54, an active layer 56, and source and drain electrodes 58 and 60, is disposed at a crossing of the gate line 52 and the data line 62. The pixel region “P” includes a reflective portion “C” and a transmissive portion “D.” A reflective electrode 64 and a transparent electrode 66 correspond to the reflective portion “C” and the transmissive portion “D,” respectively. The reflective electrode 64 having a transmissive hole 64a can be formed over the transparent electrode 66. A metal pattern 63 with an island shape overlaps a portion of the gate line 52 and contacts the reflective electrode 64 or the transparent electrode 66. The metal pattern 63 and the overlapped portion of the gate line 52 constitute a storage capacitor “CST.”
FIGS. 2 and 3 are schematic cross-sectional views, which are taken along a line “I—I” of FIG. 1, showing a transflective liquid crystal display device according to first and second embodiments of the related art, respectively.
In FIGS. 2 and 3, first and second substrates 50 and 80 face into and are spaced apart from each other. The first and second substrates 50 and 80 include a plurality of pixel regions “P.” A gate line (not shown) and a data 62 line crossing each other are formed on an inner surface of the first substrate 50. Red, green, and blue sub-color filters 84a and 84b are formed on an inner surface of the second substrate 80, and a black matrix 82 is formed between the sub-color filters 84a and 84b. A transparent common electrode 86 is formed on the sub-color filters 84a and 84b and the black matrix 82. The pixel region “P” includes a reflective portion “C” and a transmissive portion “D.” Generally, a reflective electrode 64 corresponding to the reflective portion “C” and a transparent electrode 66 corresponding to the transmissive portion “D” are formed over an inner surface of the first substrate 50. The reflective electrode 64 having a transmissive hole “64a” can be formed over or under the transparent electrode 66.
In the transflective LCD device, it is very important to obtain an equivalent optical efficiency in the reflective and transmissive portions “C” and “D.” In FIG. 2, because the light path (the distance that light transverses when light passes through a liquid crystal layer) in the reflective portion “C” is different from that in the transmissive portion “D,” the polarization properties in the reflective and transmissive portions “C” and “D” are also different from each other. When light passes through a liquid crystal layer 90 having a thickness “d” in the transmissive portion “D,” light passing through the liquid crystal layer 90 in the reflective portion “C” is reflected at the reflective electrode 64 and then passes through the liquid crystal layer 90 again. Accordingly, light path in the reflective portion “C” is twice of that in the transmissive portion “D”. Thus, light has different polarization properties in the reflective and transmissive portions “C” and “D,” thereby a difference in light efficiency is generated.
To solve this problem, as shown in FIG. 3, an insulating layer 63 in the transmissive portion “D” has an open portion 61 so that light path in the reflective portion “C” can be the same as that in the transmissive portion “D.” When the liquid crystal layer 90 in the reflective portion “C” has a first thickness of “d,” the liquid crystal layer 90 in the transmissive portion “D” has a second thickness of “2d.” In other words, the liquid crystal layer 90 has a dual cell gap.
However, even though light efficiency of the reflective portion “C” is the same as that of the transmissive portion “D” due to the dual cell gap, uniform color reproducibility cannot be obtained. The sub-color filter 84a and 84b in the reflective portion “C” has the same thickness as that in the transmissive portion “D.” Light passes through the sub-color filter 84a and 84b twice in the reflective portion “C,” while light passes through the sub-color filter 84a and 84b just once in the transmissive portion “D.” Accordingly, even though light passing through the transmissive portion “D” is brighter than light reflected from the reflective portion “C,” light emitted from the reflective portion “C” has higher color reproducibility than that emitted from the transmissive portion “D.” To solve this problem, a method that a sub-color filter having a dual thickness in the reflective and transmissive portions is suggested in Korean Patent Application No. 2000-9979.
FIG. 4 is a schematic cross-sectional view, which is taken along a line “I—I” of FIG. 1, showing a transflective liquid crystal display device according to a third embodiment of the related art. First and second substrates 50 and 80 having a pixel region “P” face into and are spaced apart from each other, and a liquid crystal layer 90 is interposed therebetween. The pixel region “P” includes a reflective portion “C” and a transmissive portion “D.” A black matrix 92 is formed on an inner surface of the second substrate 80 at a border of the pixel region “P.” A transparent buffer layer 94 corresponding to the reflective portion “C” is formed on the black matrix 82. Red and green sub-color filters 96a and 96b are formed on the buffer layer 94 in the pixel region “P.” A common electrode 98 is sequentially formed on the buffer layer 94.
A reflective electrode 64 corresponding to the reflective portion “C” and a transparent electrode 66 corresponding to the transmissive portion “D” are formed on an inner surface of the first substrate 50. Generally, the reflective electrode 64 having a transmissive hole 64a is formed under the transparent electrode 66. Because an insulating layer 63 under the reflective electrode 64 has an open portion 61 corresponding to the transmissive hole 64a, a first thickness “d1” of the liquid crystal layer 90 in the reflective portion “C” may be a half of a second thickness “d2” of the liquid crystal layer 90 in the transmissive portion “D.” That is, the second thickness “d2” of the liquid crystal layer 90 in the transmissive portion “D” is substantially twice of the first thickness “d1” of the liquid crystal layer 90 in the reflective portion “C.” Each of the sub-color filters 96a and 96b has a thickness ratio of 1:2 in the reflective and transmissive portions “C” and “D” due to the buffer layer 94.
FIGS. 5A to 5F are schematic cross-sectional views showing a fabricating process of a color filter layer of a transflective liquid crystal display device according to a third embodiment of the related art.
In FIG. 5A, a black matrix 92 is formed on a substrate 80 by sequentially depositing and patterning chromium oxide (CrOx) and chromium (Cr). The black matrix 92 is used for low reflectance of an LCD screen. Because the aperture ratio directly depends on the shape of the black matrix 92, the black matrix 92 is formed to cover only a portion corresponding to a switching element (not shown), a gate line (not shown) and a data line (not shown) considering preventing light leakage due to reflected light and the assembly margin of the attachment process. As a result, the substrate in a pixel region is exposed.
In FIG. 5B, a transparent thin film 93 is formed on the black matrix 92 by depositing photopolymeric polymer or organic insulating material. An inorganic insulating material also may be used for the transparent thin film 93.
In FIG. 5C, a buffer layer 94 is formed at a portion corresponding to the reflective portion “C” through a photolithographic process that eliminates the transparent thin film 93 (of FIG. 5A) corresponding to the transmissive portion “D.” As a result, the buffer layer 94 is formed on a second substrate 80 corresponding to the reflective portion “C.”
In FIG. 5D, a red sub-color filter 96a is formed on the buffer layer 94 by coating and patterning color resin including red dye. Since the color resin fills a portion corresponding to the transmissive portion “D” where the buffer layer 94 is not formed, the red sub-color filter 96a is formed to correspond to one pixel region “P” including the reflective and transmissive portions “C” and “D.”
In FIG. 5E, similar to the red sub-color filter 96a, a green sub-color filter 96b is formed on the buffer layer 94 by coating and patterning color resin including green dye.
In FIG. 5F, similar to the red and green sub-color filters 96a and 96b, a blue sub-color filter 96c is formed on the buffer layer 94 by coating and patterning color resin including blue dye, thereby a color filter layer 96 including red, green and blue sub-color filters 96a, 96b and 96c completed. A common electrode 98 is formed on the color filter layer 96 by depositing one of a transparent conductive metallic material group including indium-tin-oxide (ITO) and indium-zinc-oxide (IZO). A planarization layer (not shown) may be formed between the color filter layer 96 and the common electrode 98.
Referring again to FIG. 4, the insulating layer 63 having the open portion 61 is formed to obtain a cell gap ratio of 1:2 in the reflective and transmissive portions “C” and “D,” and the buffer layer 94 is formed to obtain a thickness ratio of 1:2 of the color filter layer 96 in the reflective and transmissive portions “C” and “D.” However, even though equivalent optical efficiency and color reproducibility is obtained in the reflective and transmissive portions, the fabrication process for the dual cell gap ratio of 1:2 and the thickness ratio of 1:2 is very complex. Moreover, because excess organic materials are used, the production cost increases.